1. Technical Field
The present disclosure relates to a method of manufacturing a unit cell of a solid oxide fuel cell using a decalcomania process in which an anode, electrolyte, cathode, and interconnect are stacked on a substrate when manufacturing unit cells of solid oxide fuel cells having a variety of shapes, such as a planar type, a horizontal pipe type, a tubular type, a segmented type, and the like. More particularly, the present disclosure relates to a method of manufacturing a unit cell of a solid oxide fuel cell using a decalcomania process in which components of each unit cell, such as an anode, cathode, electrolyte, interconnect and the like, may be deposited in a desired shape by the decalcomania process through deposition or coating, in manufacture of solid oxide fuel cells having a variety of shapes according to lamination and arrangement of unit cells, so that the components of the unit cell having a large scale or complicated structure can be deposited without being limited in terms of size or shape, the thickness of the components in the unit cell can be easily controlled depending on the stacked number of transfer paper sheets, and a coating film can be formed on a substrate at lower cost.
2. Description of the Related Art
In a Solid Oxide Fuel Cell (hereinafter, referred to as “SOFC”), which has attracted attention as a next generation energy conversion device, a unit cell is generally constructed using zirconia as an electrolyte and includes an anode and a cathode (air electrode), and such unit cells are combined to form a stack. Advantageously, SOFCs can utilize hydrocarbons as well as hydrogen, eliminating the need for reformation of fuel gas, and have the highest known power generation efficiency. In addition, SOFCs are an environmentally friendly energy conversion device which does not release NOx, SOx, or the like.
SOFCs can be classified into a planar type, a horizontal pipe type, a tubular type, and a segmented type according to the shape of the unit cell and arrangement of stacks.
The planar type has a short current path, which advantageously results in higher efficiency than other types and higher power density than the tubular type. Since most of the components therein are ceramic composites, however, the planar type is brittle and subject to fracture. Moreover, the planar type is disadvantageous in that it is difficult to realize a large scale unit cell and to prevent gas from escaping due to structural characteristics of the unit cell.
On the contrary, the tubular type is close to commercial distribution, since the tubular type has structural characteristics providing high resistance to thermal impact while allowing easy sealing of the unit cell and easy manufacture of a large scale unit cell. However, the tubular type has low power density per unit area and requires a high-cost manufacturing process.
The horizontal pipe type is designed to solve the structural problems of the planar type and the tubular type. The horizontal pipe type is configured to solve both the problems of the planar type and the low power density of the tubular type.
In the segmented type, unit cells are connected in series on a substrate, thereby providing increased stacking efficiency, a reduction in current-resistance loss due to a short interval between the unit cells, and excellent mechanical strength. However, a long current path through an anode and a cathode in the segmented type disadvantageously causes internal resistance loss.
In manufacture of the SOFC unit cells having various configurations as described above, methods of depositing or coating the components of the unit cell on a substrate are divided as follows.
Gas phase coating or deposition includes a variety of processes, such as Electrochemical Vapor Deposition (EVD), Chemical Vapor Deposition (CVD), sputtering, plasma spraying, and the like. However, these processes have problems of limited starting materials and sample size, a slow film growth rate which makes it difficult to manufacture a thick sample, low adhesion to a substrate, and economical problems such as an increase in process cost due to expensive equipment, and the like.
Liquid phase coating or deposition is a relatively easy process and includes screen printing, tape casting, spin coating, dip coating, slip coating, electrochemical coating, and the like.
Inter alia, screen printing employing pastes is generally used. However, screen printing cannot be applied to either the tubular type or the horizontal pipe type due to a limit in size and shape of a coating substrate.
Therefore, the tubular type and the horizontal pipe type close to commercial distribution are generally manufactured by dip coating plasma spraying. However, dip coating plasma spraying has problems such as a difficulty in control of film thickness, complicated process, and high manufacturing costs.
To solve such problems, the inventor of the present disclosure suggests the use of a decalcomania process as a new film formation process, which is simple and can provide a thick or uniform film.